Research article No long-term costs of meristem allocation to ¯owering in stoloniferous Trifolium species HEIDRUN HUBER 1,2 * and HEINJO J. DURING 1 1 Department of Plant Sciences, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands; 2 Department of Ecology and Evolutionary Biology, Brown University, Box G-W-101, Providence, RI 02912, USA (*author for correspondence, tel.: +401-863-2100; fax: +401-863-3435; e-mail: heidrun_huber@brown.edu) Received 2 March 2000; accepted 25 May 2001 Co-ordinating editor: J. Tuomi Abstract. Clonal plants propagate by means of clonal growth and sexual reproduction. The commitment of meristems to branching and ¯owering govern the expression of these two mutually exclusive life-history functions. We used a modelling and an experimental approach to examine the consequences of a structural trade-o between ¯owering and clonal growth on future growth and ®tness in stoloniferous species with a determinate module architecture. The model revealed negative eects of ¯owering on vegetative growth due to a structural trade-o at the meristem level. Total fecundity was maximized at intermediate ¯owering frequencies. In addition, optimal meristem commitment to ¯owering depended strongly on the time available for growth and reproduction. This indicates an interaction between optimal ¯owering frequency, the length of the growing period and the rate of ontogenetic development. The greenhouse study made use of 15 genotypes of two closely related, stoloniferous Trifolium species. Despite the existence of a structural trade-o at the meristem level, we found no evidence for costs of ¯owering on the whole-plant level. High allo- cation to ¯owering did not result in reduced plant performance (biomass and module production) and total fecundity, indicating that there were no demographic costs of meristem investment to dierent life-history functions. Flowering frequencies never exceeded the model prediction for optimal commitment of meristems to sexual reproduction, suggesting strong past selection to eliminate high levels of meristem allocation to ¯owering. Hence, clonal growth seems to have evolutionary priority over sexual reproduction in our species. Key words: clonal growth, meristem allocation, sexual reproduction, trade-o, Trifolium Introduction Clonal growth of plants implies the asexual, vegetative production of geneti- cally identical, potentially independent ospring individuals. Most clonal plants are also capable of sexual reproduction by ¯owering and seed set. Clonal growth allows genotypes to multiply and to spread in their local environment. Despite the prevalent contribution of vegetative propagation to population growth and development, seed dispersal and seedling recruitment are crucial to clonal plant species in terms of maintenance of genetic diversity in clonal plant Evolutionary Ecology 14: 731±748, 2001. Ó 2001 Kluwer Academic Publishers. Printed in the Netherlands.